This invention relates to a fuel supply apparatus for use with an engine which uses gaseous fuel such as hydrogen gas.
In recent years, there has been developed a gaseous fuel engine which uses combustible gas such as hydrogen gas as fuel. When the gaseous fuel is used, its volume rate is remarkably larger than gasoline. Accordingly, if the engine is constructed such that the gaseous fuel is mixed with air in an intake passage and supplied to a combustion chamber, an amount of air admitted into the cylinder is greatly reduced to thereby cause a reduction in an engine output particularly when a large amount of fuel is supplied. Even if the gaseous fuel is supplied into the combustion chamber through a passage different from the one to supply the air to the combustion chamber, the volumetric efficiency of the air cannot be made large when the gaseous fuel having a large volume rate exists in the combustion chamber. Thus, the engine output cannot be increased.
As a measure against the above problem, the following arrangement is made in an apparatus disclosed in, for example, Japanese Examined Patent Publication No. 58-36172. Two separate passages are provided: an intake passage to supply the air and a hydrogen supply passage to supply the hydrogen gas. An inlet valve and a hydrogen supply valve are provided respectively at the intake passage and the hydrogen supply passage. The inlet valve is closed at a bottom dead center and the hydrogen supply valve is opened at the bottom dead center, so that opening periods of these valves do not overlap each other. The hydrogen gas Is supplied into the combustion chamber at a pressure higher than a pressure in the cylinder while the hydrogen supply valve is opened, Further, in an apparatus disclosed in Japanese Examined Patent Publication No. 1-23659, there are provided an inlet valve for admitting the air into a combustion chamber and a fuel supply valve for supplying the pressurized gaseous fuel, and the fuel supply valve is opened near a bottom .dead center almost before completion of an air intake stroke.
The apparatuses disclosed In the above publications are advantageous in increasing the engine output in the high induction zone by increasing the volumetric efficiency of the air since the pressurized gaseous fuel is supplied to the combustion chamber after the air intake stroke is almost completed. However, since the fuel is supplied until the pressure in the cylinder increases to a substantially high level in the compression stroke, the apparatus is required to supply the gaseous fuel at the substantially high pres sure so as to supply the fuel into the cylinder against the pressure in the cylinder during the compression stroke. The fuel supply amount is controlled by means of a flow control valve or the like arranged along a fuel supply pipe. However, it is difficult to supply the required amount of fuel accurately in the case where the amount of gaseous fuel having the large volume rate is adjusted over a range including a zone where the fuel supply amount is large while supplying the fuel under the high pressure as above. Particularly, in the low induction zone where the fuel supply amount is small, the error of the fuel supply amount becomes large, thereby standing as a hindrance to the combustion stability.